Analytische Chemie
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Alkaline earth metal fluoride nanoparticles have been investigated for application in wood protection. Sols of MgF2 and CaF2 were synthesized and their efficacy was tested against fungi and termites (Rehmer 2016, Krahl et al. 2016). The sols were characterized by XRD and SEM. The wood specimens were vacuum impregnated with nanoparticles and then exposed to fungi and termites according to EU certified test conditions. Our results show that wood impregnated with metal fluoride nanoparticles significantly reduce cellulose hydrolysis by fungi and termites. The wood samples were exposed to brown-rot fungi; Coniophora puteana and Poria placenta. Between the two fungi, the overall mass lost due to fungal degradation was lower for treated (MgF2 and CaF2) wood samples exposed to Coniophora puteana. Thus, the metal fluoride nanoparticles impregnated in the wood samples were more efficient in reducing cellulose degradation from Coniophora puteana than from Poria placenta. However the mass loss in samples treated with MgF2 was similar to those treated with CaF2, irrespective of type of fungi. Therefore, it is likely that fungal degradation in treated samples was dependent on the biocidal action of fluorides rather than on the differences in chemical and physical properties of MgF2 and CaF2, respectively. Conversely, for termite exposure, wood samples treated with MgF2 had lower cellulose degradation compared to those treated with CaF2. A possible explanation for this difference in results could be fungi and termites use separate mechanisms for cellulose hydrolysis which will be further investigated. Future experiments include testing the leaching potential of MgF2 and CaF2 nanoparticles from wood. The results from the leaching experiment will test if metal fluoride nanoparticles can provide long-term and environmentally safe protection to wood.
Odor Perception by Dogs: Evaluating Two Training Approaches for Odor Learning of Sniffer Dogs
(2017)
In this study, a standardized experimental set-up with various combinations of herbs as odor sources was designed. Two training approaches for sniffer dogs were compared; first, Training with a pure reference odor, and second, training with a variety of odor mixtures with the target odor as a common denominator. The ability of the dogs to identify the target odor in a new context was tested. Six different herbs (basil, St. John’s wort, dandelion, marjoram, parsley, ribwort) were chosen to produce reference materials in various mixtures with (positive) and without (negative)chamomile as the target odor source. The dogs were trained to show 1 of 2 different behaviors, 1 for the positive, and 1 for the negative sample as a yes/no task. Tests were double blind with one sample presented at a time. In both training approaches, dogs were able to detect chamomile as the target odor in any presented mixture with an average sensitivity of 72% and a specificity of 84%. Dogs trained with odor mixture containing the target odor had more correct indications in the transfer task.
Since 1999 there has been a continuous development of non-destructive head check inspection. Especially in case of modern rail inspection systems, high demands on a fast, detailed detection and classification of defects called for improved testing methods. Due to the large amount of different rail types and profiles, the adaptation and optimization of algorithms is still in progress. Additional data analysis is under devel-opment for combined eddy current and ultrasonic inspection methods. This presentation gives an over-view of further enhancement and linking of testing systems as well as data processing. Main foci of the development are an improved sensitivity and an increased reliability of the testing results. Also, addi-tional information can be obtained like determination of local hardness and roughness of the rail as well as an enhanced resolution for locating of defects which will be part of the presented work.
In vielen Bereichen der Technik haben Konstruktionen unter Einsatz von CFK-Bauteilen und Komponenten die klassischen Metalle abgelöst. Die zerstörungsfreie Prüfung solcher CFK-Bauteile gewinnt somit zunehmend an Bedeutung. Ein mögliches Prüfverfahren ist dabei die Wirbelstromprüfung. Aufgrund der relativ geringen elektrischen Leitfähigkeit von CFK-Komponenten kommt hierbei häufig die sogenannte HF-Wirbelstromprüfung zum Einsatz.
In verschiedenen Untersuchungen der BAM konnten jedoch auch mit Wirbelstromprüfsystemen in niedrigen Frequenzbereichen gute Ergebnisse erzielt werden. Um die Möglichkeiten und Grenzen dieser konventionellen Wirbelstromprüfung auszuloten, wurden Messungen an Versuchskörpern durchgeführt, welche bereits bei der Validierung der Blitz- und Lock-in-Thermografie für neue Verfahrensnormen erfolgreich eingesetzt wurden. Ein Typ dieser Versuchskörper sind Flachproben aus CFK von 6 mm Dicke. In diesen wurden Flachbodenbohrungen mit Durchmessern zwischen 4 mm und 24 mm eingebracht. Die Restwandstärken liegen zwischen 0,06 mm und 3,66 mm. Ein weiterer CFK-Versuchskörper hat die Geometrie eines Stufenkeiles. Bei verschiedenen Stufenkeilen sind Wanddicken zwischen 1,4 mm und 5,4 mm realisiert worden. In diesen wurden künstliche quadratische Delaminationen mit Kantenlängen zwischen 2 mm und 20 mm eingebracht. Die Ergebnisse der Wirbelstromprüfung werden denen der aktiven Thermografie gegenübergestellt.
Zur Nachbildung von Kompositwerkstoffen wurden die flachen Versuchskörper mit geeigneten Versuchskörpern aus Aluminium und Stahl kombiniert. Die Wirbelstromprüfungen wurden mit einem handelsüblichen Prüfgerät im Frequenzbereich zwischen 500 Hz und 3 MHz und entsprechend angepassten Sensoren durchgeführt.
Main concept of magnetism and, therefore, of magnetic imaging can be subdivided into different levels, macroscopic, magnetic domain, and atomic. While conventional sensor solutions cover only the macroscopic level, the spatial resolution of GMR (Giant Magneto Resistance) sensors go down to the domain scale. In addition, those low cost sensors are well suited for automotive and industrial applications, particularly high-speed solutions. Main reason is their outstanding performance in terms of high spatial resolution, high accuracy, high bandwidth combined with field sensitivity, energy efficiency and durability.
In contrast to industrial use, down to the present day GMR sensors do not get beyond scientific scope in case of non-destructive testing (NDT) applications. Nevertheless, there are scientific and industrial NDT applications in which adapted GMR sensor can be promising compared to the conventional NDT methods.
This contribution summarizes findings at the BAM over the last decade which demonstrates the preeminent properties of GMR-based testing solutions. This comprises the active and passive testing of different materials with hidden defects and flaws near geometric boundaries like edges where conventional methods meet their limits. Another promising application for adapted GMR sensors is the characterization of magnetic materials, where the sensors provide additional information on microstructure, mechanical stress state, phase transformations and their interaction with magnetic fields. The examples show the need and benefit of NDT adapted GMR sensors.
Pulse and flash thermography are experimental techniques which are widely used in the field of non-destructive evaluation for materials characterization and defect detection. We recently showed that it is possible to quantitatively determine the thickness of semitransparent polymeric solids by fitting of results of an analytical model to experimental flash thermography data, for both transmission and reflection geometry. However, depending on the chosen experimental geometry, different effective optical absorption coefficients (i.e., penetration depths of the heating light) had to be utilized in the model in order to properly fit the experimental data. Here we show that this effect is caused by the wavelength dependency of the absorption coefficient of the sample material. We present an extension of the analytical model to incorporate this dispersion. Even accounting for only two different values of the absorption coefficient, the experimental results from both measurement geometries can be fitted by a single set of absorption coefficients. Additionally, the deviations between experimental data and fit are reduced compared to a single optimized effective absorption coefficient.
This work is part of the ZIM-project KF2201089AT4 and is funded by the German Federal Ministry for Economic Affairs and Energy due to an order of the German Bundestag.
The use of composite pressure vessels instead of conventional vessels made of steel or aluminum grew strongly over the last decade. The reason for this trend is the tremendous weight saving in case of composite vessels. However, the long-time behavior is not fully understood for filling and discharging cycles and creep strength and their influence on the CFRP coating (carbon fiber reinforced plastics) and the internal liner (steel, aluminum, or plastics) [1]. The CFRP ensures the pressure resistance while the inner liner is used as container for liquid or gas. To overcome the missing knowledge of ageing BAM started an internal project to investigate degradation of these material systems [2]. Therefore, applicable testing methods are needed. Normally, high-frequency eddy current testing (HF-ET, f > 10 MHz) is deployed for CFRP due to its low conductivity of the fiber, which is in the order of 0.01 MS/s, and the capacitive coupling between the fibers. Nevertheless, in some cases conventional ET can be applied. We show a concise summary of studies on the application of conventional ET of composite pressure vessels.